Methods and apparatus for de-watering sludge

ABSTRACT

An apparatus for de-watering sludge. A main shaft is rotated about a longitudinal axis at a first rate. A screw shaft coupled to the main shaft is rotated about the longitudinal axis at the first rate. Screw flighting coupled to the screw shaft is rotated about the longitudinal axis at the first rate. A first and second stage drum are rotated about the longitudinal axis at a second rate. Sludge is introduced to a first area defined by an outer surface of the screw shaft and an inner surface of the first stage drum. Moisture is removed from the sludge through a first slot coupled to the first stage drum. The sludge is transported with the screw flighting from the first area to a second area defined by an outer surface of the screw shaft and an inner surface of the second stage drum, the second area being larger than the first area. Moisture is removed from the sludge through a second slot coupled to the second stage drum.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the fields ofde-watering sludge. More particularly, it concerns methods and apparatusfor de-watering sludge by utilizing a multi-stage, rotating drumtechnique.

[0003] 2. Description of Related Art

[0004] The ability to remove water from products such as waste productshas long been recognized as useful. Removing water from sludge, and moreparticularly, sewage sludge, greatly reduces the weight of material tobe transported for disposal and/or use. Additionally, de-watering sludgemay facilitate the processing of sludge into soil conditioners andfertilizers.

[0005] De-watering of sludge has been accomplished in the past byvarious methods, including open-air drying, vacuum filtration,centrifugation, mechanical pressing, and other mechanical separation.Although each has utilized at least a degree of usefulness, room forsignificant improvement remains.

[0006] U.S. Pat. No. 3,695,173 describes a technique for sludgede-watering. There, de-watering is achieved as sludge is moved through afilter de-watering unit, where squeezing and pressing takes place. Thesqueezing and pressing forces most of the liquid or water through afiltering medium or slots. Cleaning blades or brushes are used preventclogging and interruption of continuous filtration or de-watering.Although this technique may be useful for de-watering certain types ofsludge, problems remain. For instance, if there is too little sludgebeing fed into the device, the sludge may not be squeezed enough.Consequently it may not be dried sufficiently. Further, if too muchsludge enters the device, it may come under too much pressure and may beforced out through the device. Consequently, sludge may be lost and mayneed to be re-circulated. Still further, if a polymer has been used onthe sludge being de-watered, this system may, if subjected to highpressures, break polymer bonds and may therefore not be effective inde-watering sewage sludge, especially re-circulated sludge.

[0007] U.S. Pat. No. 4,286,512 describes another technique that may beused to remove liquid from a material. There, a screw press is used forpressing liquid from fibrous slurries, such as paper pulp, sludge, orsedimentation. Material is fed into the press at one end of a rotatingpress screw. The core of the screw has an increasing diameter such thatthe space defined between the core and wall of a drum graduallydecreases so as to aid in the pressing process. A rotating drum rotatesabout the core to further aid in the draining of liquid pressed from theslurry due to the action of the press-screw. Although this techniquealso may be useful for de-watering certain types of sludge, similarproblems remain due mostly to the fact that this technique relies uponpressing of the sludge to achieve drying. Again, if there is too littlesludge being fed into the device, the sludge may not be squeezed enough.On the other hand, if too much sludge enters the device, it may comeunder too much pressure and may be prematurely forced out of the device.Consequently, sludge may be lost and may need to be re-circulated. Stillfurther, if a polymer has been used on the sludge being de-watered, thissystem may, if subjected to high pressures, break polymer bonds. Forthis reason, such a system may not be effective in de-watering sewagesludge, especially re-circulated sludge.

[0008] U.S. Pat. No. 4,202,773 describes another technique that may beused to de-water sludge. There, clarifier sludge may be de-watered bypassing it through an inner centrifuge drum and then to outer seconddrum having a diameter about twice that of the first drum. In each drum,wipers or scrapers displace solids. Each drum is unperforated, the outerdrum is conical over its entire length, and the inner drum is conical inpart or in whole. Although this system may be useful for de-wateringcertain materials, problems remain. For instance, it appears that sludgeis spun at relatively high speeds to insure that solids within thesludge are displaced and so that sludge does not overly mix with waterand liquids being extracted. Further, it appears that this device maysubject sludge to great forces, particularly after transfer to thelarger outer centrifuge, so that polymer bonds may be broken.

[0009] Problems enumerated above are not intended to be exhaustive butrather are among several that tend to impair the effectiveness ofpreviously known devices for removing water and liquids from sludge.Other noteworthy problems may also exist; however, those presented aboveshould be sufficient to demonstrate that devices appearing in the arthave not been altogether satisfactory.

SUMMARY OF THE INVENTION

[0010] In one respect, the invention is an apparatus for de-wateringsludge, including an outer housing, a main shaft, a screw shaft, a firststage drum, a second stage drum, an inlet, and screw flighting. Theouter housing defines a longitudinal axis. The main shaft is configuredto rotate about the longitudinal axis. The screw shaft is coupled to themain shaft and is configured to rotate about the longitudinal axis. Thefirst stage drum is positioned between the outer housing and the screwshaft. The first stage drum is configured to rotate about thelongitudinal axis, and the first stage drum has a first drum diameter.The second stage drum is coupled to the first stage drum. The secondstage drum is configured to rotate about the longitudinal axis, and thesecond stage drum has a second drum diameter greater than the first drumdiameter. The inlet is configured to introduce the sludge to a firstarea defined by an outer surface of the screw shaft and an inner surfaceof the first stage drum. The screw flighting is coupled to the screwshaft. The screw flighting is configured to rotate about thelongitudinal axis to transport the sludge longitudinally from the firstarea to a second area defined by an outer surface of the screw shaft andan inner surface of the second stage drum, the second area being largerthan the first area.

[0011] In other respects, the main shaft and the screw shaft may each beconfigured to rotate at a first rate, and the first stage drum and thesecond stage drum may each be configured to rotate at a second rate. Thefirst rate may be less than the second rate. The first rate may equalthe second rate. The main shaft may have a substantially constant outerdiameter, and the screw shaft may have a substantially constant outerdiameter. The apparatus may also include wiper coupled to the screwflighting. The wiper may be configured to clean an inner surface of thefirst stage drum and to roll the sludge from the first area to thesecond area. The first stage drum may include a first slot, and thesecond stage drum may include a second slot. Each of the first andsecond slots may include a smaller opening on an inner surface of thedrums than on an outer surface of the drums. The first slot may besmaller than the second slot. The first slot may be about the same sizeas the second slot. The apparatus may also include a third stage drum.The third stage drum may be coupled to the second stage drum. The thirdstage drum may be configured to rotate about the longitudinal axis. Thethird stage drum may have a third drum diameter greater than the seconddrum diameter. The screw flighting may be configured to transport thesludge longitudinally from the second area to a third area defined by anouter surface of the screw shaft and an inner surface of the third stagedrum, the third area being larger than the second area. The apparatusmay also include a fourth stage drum. The fourth stage drum may becoupled to the third stage drum. The fourth stage drum may be configuredto rotate about the longitudinal axis. The fourth stage drum may have afourth drum diameter greater than the third drum diameter. The screwflighting may be configured to transport the sludge longitudinally fromthe third area to a fourth area defined by an outer surface of the screwshaft and an inner surface of the fourth stage drum, the fourth areabeing larger than the third area. The apparatus may also include a washnozzle coupled to the screw shaft. The outer housing may be inclined.

[0012] In another respect, the invention is an apparatus for de-wateringsludge, including an outer housing, a main shaft, a screw shaft, a drum,an inlet, screw fighting, and a wiper. The outer housing defines alongitudinal axis. The main shaft is configured to rotate about thelongitudinal axis. The screw shaft is coupled to the main shaft and isconfigured to rotate about the longitudinal axis. The drum is positionedbetween the outer housing and the screw shaft and is configured torotate about the longitudinal axis. The drum has a slot including asmaller opening on an inner surface of the drum than on an outer surfaceof the drum. The inlet is configured to introduce the sludge to an areadefined by an outer surface of the screw shaft and an inner surface ofthe drum. The screw flighting is coupled to the screw shaft and isconfigured to rotate about the longitudinal axis to transport the sludgelongitudinally along the drum. The wiper is coupled to the screwflighting and is configured to clean an inner surface of the drum and toroll the sludge along the drum.

[0013] In another respect, the invention is an apparatus for de-wateringsludge including an outer housing, a main shaft, a screw shaft, a washnozzle, a first stage drum, a second stage drum, an inlet, a screwflighting, and a wiper. The outer housing defines a longitudinal axis.The main shaft is configured to rotate about the longitudinal axis. Thescrew shaft is coupled to the main shaft and is configured to rotateabout the longitudinal axis. The wash nozzle is coupled to the screwshaft. The first stage drum is positioned between the outer housing andthe screw shaft. The first stage drum is configured to rotate about thelongitudinal axis, and the first stage drum has a first drum diameterand a first slot. The first slot includes a smaller opening on an innersurface of the first stage drum than on an outer surface of the firststage drum. The second stage drum is coupled to the first stage drum.The second stage drum is configured to rotate about the longitudinalaxis, and the second stage drum has a second drum diameter greater thanthe first drum diameter and a second slot. The second slot includes asmaller opening on an inner surface of the second stage drum than on anouter surface of the second stage drum. The inlet is configured tointroduce the sludge to a first area defined by an outer surface of thescrew shaft and an inner surface of the first stage drum. The screwflighting is coupled to the screw shaft. The screw flighting isconfigured to rotate about the longitudinal axis to transport the sludgelongitudinally from the first area to a second area defined by an outersurface of the screw shaft and an inner surface of the second stagedrum, the second area being larger than the first area. The wiper iscoupled to the screw flighting and is configured to clean an innersurface of the first stage drum and to roll the sludge from the firstarea to the second area.

[0014] In other respects, the main shaft and the screw shaft may each beconfigured to rotate at a first rate, and the first stage drum and thesecond stage drum may each be configured to rotate at a second rate. Thefirst rate may be less than the second rate. The first rate may equalthe second rate.

[0015] In another respect, the invention is a method for de-wateringsludge. A main shaft is rotated about a longitudinal axis at a firstrate. A screw shaft coupled to the main shaft is rotated about thelongitudinal axis at the first rate. Screw flighting coupled to thescrew shaft is rotated about the longitudinal axis at the first rate. Afirst and second stage drum are rotated about the longitudinal axis at asecond rate. The first and second stage drums are positioned between anouter housing and the screw shaft. Sludge is introduced to a first areadefined by an outer surface of the screw shaft and an inner surface ofthe first stage drum. Moisture is removed from the sludge through afirst slot coupled to the first stage drum. The sludge is transportedwith the screw flighting from the first area to a second area defined byan outer surface of the screw shaft and an inner surface of the secondstage drum, the second area being larger than the first area. Moistureis removed from the sludge through a second slot coupled to the secondstage drum.

[0016] In other respects, the first rate may be less than the secondrate. The first rate may equal the second rate. The method may alsoinclude cleaning an inner surface of the first stage drum with a wipercoupled to the screw flighting. The method may also include cleaning aninner surface of the first stage drum with a wash nozzle coupled to thescrew shaft. The method may also include rotating a third stage drumabout the longitudinal axis at the second rate, the third stage drumbeing positioned between an outer housing and the screw shaft. Thesludge may be transported with the screw flighting from the second areato a third area defined by an outer surface of the screw shaft and aninner surface of the third stage drum, the third area being larger thanthe second area. Moisture may be removed from the sludge through a thirdslot coupled to the third stage drum. The method may also includerotating a fourth stage drum about the longitudinal axis at the secondrate, the fourth stage drum being positioned between an outer housingand the screw shaft. The sludge may be transported with the screwflighting from the third area to a fourth area defined by an outersurface of the screw shaft and an inner surface of the fourth stagedrum, the fourth area being larger than the third area. Moisture may beremoved from the sludge through a fourth slot coupled to the fourthstage drum.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following drawings form part of the present specification andare included to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein.

[0018]FIG. 1 shows a de-watering apparatus according to one embodimentof the present disclosure.

[0019]FIG. 2 shows an expanded view of an inlet end of a de-wateringapparatus according to one embodiment of the present disclosure.

[0020]FIG. 2A shows an expanded view of an inlet end of a de-wateringapparatus according to an alternative embodiment of the presentdisclosure.

[0021]FIG. 3 shows an expanded view of an outlet end of a de-wateringapparatus according to one embodiment of the present disclosure.

[0022]FIG. 4 shows an expanded view of an inner section of a de-wateringapparatus according to one embodiment of the present disclosure.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0023] Embodiments of devices for de-watering material are illustratedin FIGS. 1-4. As illustrated, the apparatus includes a stationary outerhousing 1, which may enclose, partially or completely, the contents ofthe apparatus. In one embodiment, outer housing 1 may be fabricated froma material such as carbon or stainless steel. Sealing may be with thebenefit of the present disclosure, will understand that main shaft 7 maybe constructed without a hollow portion. In such an embodiment, sludgemay be introduced directly into the apparatus by a separate feed tube orany other suitable manner known in the art.

[0024] With reference to FIGS. 2 and 2A, it may be seen that slurry maybe fed out inlet holes 12, located around a hollow portion of shaft 7,and into a space defined by an outer surface of rotating screw shaft 8and first stage drum 9. Specifically, in FIG. 2, slurry may be fed froma hollow portion of main shaft 7, out inlet hole 12 (illustrated as thecenter hole), and into a space defined between main shaft 7 and screwshaft 8. From that space, the slurry may be fed to an area between screwshaft 8 and first stage drum 9 via additional inlet holes 12,illustrated as being to the left and right of the center inlet openingof FIG. 2. In FIG. 2A, slurry may be fed form a hollow portion of mainshaft 7, out inlet holes 12 directly to an area between screw shaft 8and first stage drum 9. The size of inlet holes 12 and the spacingbetween main shaft 7, screw shaft 8, and first drum 9 may be configuredand adjusted appropriately so as to introduce a controlled volume ofsludge into the apparatus at a given time. Specifically, the size of theinlet holes and the spacing of the components may all be configured soas to effectively restrict the amount of sludge entering the device.This feature advantageously allows a user to control the incoming volumeof sludge so that more moisture may be removed from the sludge. Inparticular, without being bound by theory, it is believed that bylimiting the volume of incoming sludge (relative to the components ofthe apparatus), one may achieve greater de-watering than possible withprevious devices. In one embodiment, utilizing an apparatusapproximately having a housing about 3 feet wide and about 20 feet long,with inlet openings 12 having a diameter of about 2 inches, a main shaft7 having a diameter of about 4 inches, a screw shaft 8 having a diameterof about 8.5 inches, and a first stage drum 9 having an inner diameterof about 12 inches, sludge has been favorably de-watered. It iscontemplated that with a differently sized apparatus, differentcontrolled volumes may be utilized by adjusting the spacing between thecomponents and by appropriately sizing inlet holes 12. In such a manner,the incoming volume may be controlled so as to optimize the de-wateringprocess.

[0025] In the illustrated embodiment, screw shaft 8 may be coupled tomain shaft 7. In one embodiment, screw shaft 8 and main shaft 7 mayrotate at the same angular velocity, but in other embodiments, therotation may be suitably de-coupled so that a differential rotation ratemay be achieved. Drums 9, including first stage drum 9, second stagedrunk 9A, third stage drum 9B, and fourth stage drum 9C, may be held inplace and may be rotated by bearing and seal assembly 27. In theillustrated embodiment, this bearing is on the same centerline asbearing 14. Thus, main shaft 7, screw shaft 8 and drums 9 may all rotateon the same centerline, longitudinal axis 18.

[0026] One or more sets of screw fighting 10 may be coupled to screwshaft 8. In one embodiment, screw fighting 10 may be integral with screwshaft 8. Although various materials may be used, the screw lighting ofthe illustrated embodiment may be constructed from stainless steel.Screw fighting 10 may be configured to form one or more containmentareas between screw shaft 8, drums 9-9C, and screw flighting 10. Asdescribed above, the spacing of such elements controls, in part, thevolume of sludge entering and traveling through the apparatus at a giventime, and therefore, may influence the effectiveness of the de-wateringprocess.

[0027] In one embodiment, an outer edge of screw fighting 10 may includea wiper 11. Wiper 11 may be configured to continuously clean an innersurface of any one or all of drums 9, 9A, 9B, and 9C as the screw shaft8, screw fighting 10 and wiper 11, rotate. In one embodiment, drums 9,9A, 9B, and 9C may rotate at a different speed/speeds than screw shaft8, screw fighting 10, and wiper 11—such differential speeds may, amongother things, facilitate the cleaning of the drums via wiper 11 and thetransfer of sludge through drums 9-9C. The shape of wiper 11 may beconfigured so that it not only cleans the inside surface of drums 9-9C,but also is so that it lifts sludge off of the drums and rolls thesludge as it moves along the inside of drums 9-9C. In lifting androlling the sludge, wiper 11 may prevent screw fighting 10 from pushingfine sludge particles out through outlet holes/slots coupled to thedrums.

[0028] With the benefit of the present disclosure, those of skill in theart will understand the rotational speeds of the main shaft 7, screwshaft 8, and drums 9-9C may vary widely according to application. In theillustrated embodiment, a suitable operational speed of drums 9-9C maybe about 200 to 500 rotations per minute. In one embodiment, screw shaft8 may rotate at about the same speed. The variation in the speed betweenthe screw shaft 8 and the rotating drums 9-9C is variable, as is thespeed of the components individually. Suitable speed controls (notillustrated) allow for screw shaft 8 and drums 9-9C to have speeds thatmay be varied independently of one other. The differential speed betweenthe screw shaft 8 and drums 9-9C controls the volume and speed at whichsludge slurry is allowed to enter the de-watering area between an outersurface of screw shaft 8 and an inner surface of drums 9-9C. Thedifferential speed between the screw shaft 8 and drums 9-9C also maydetermine the amount of time it takes the sludge to travel from theinlet end of the apparatus, adjacent inlet holes 12, through therotating drums 9-9C, and out the de-watered sludge discharge holes 13.

[0029] In the illustrated embodiment, the rotating drums 9-9C may bemade so that their inner surfaces are smooth, with holes or slots thatallow for water and other liquids to exit from the sludge being dried.The openings coupled to the drums may have a smaller opening on an innersurface than on an outer surface. In one embodiment, openings on aninner surface may range from about 0.008 inches to about 0.020 incheswhile openings on an outer surface may range from about 0.060 inches toabout 0.080 inches. With the benefit of the present disclosure, however,those having skill in the art will understand that these opening sizesmay vary widely according to application. In operation according to oneembodiment, as sludge slurry enters first stage drum 9, it may start toimmediately lose water through the holes or slots located in the firststage drum 9 wall. In the illustrated embodiment, the first stage drum 9may be relatively small, about 12 inches in inside diameter, which maybe close to the diameter of the screw shaft 8. As the sludge issubjected to a centrifugal force, it may be moved along the inside ofthe first stage drum 9.

[0030] Drums 9-9C may be rotated by a drive assembly (not shown) as isknown in the art. Such an assembly may turn the drums at a pulley orsprocket, such as sprocket 31. Main shaft 7, screw shaft 8, screwflighting 10, and wiper 11 may all be driven by a drive unit (not shown)as is known in the art via a pulley or sprocket, such as sprocket 32.The use of separate drives allow for independent operation of thecomponents.

[0031] Again, the volume, and hence, the thickness, of the initialsludge is believed to influence the effectiveness of de-watering. Thethickness may be determined by the area of the space between the screwshaft 8 and the inner surface of the drums 9-9C. As may be seen withreference to FIG. 1, this area is greater in second stage drum 9A thanin first stage drum 9. Similarly, the area in third stage drum 9B isgreater than that of second stage drum 9A. The area in fourth stage drum9C is greater than that of third stage drum 9B. In the illustratedembodiment, the sludge becomes more compact, de-watered, and firm as itenters the second stage drum 9A from first stage drum 9. In oneembodiment, second stage drum 9A may rotate at the same approximatespeed as first stage drum 9, but it may have a larger diameter. In oneembodiment, second stage drum may have a size of about 16 inches ininside diameter. This increase in diameter imparts a higher centrifugalforce on the controlled volume of sludge.

[0032] The holes/slots coupled to the wall of second stage drum 9A maybe the same size or larger than the holes/slots of first stage drum 9,giving a larger open area for liquid to be released through the drum 9Awall. As the sludge is dried in second stage drum 9A, it may be movedvia screw flighting 10 and, in embodiments utilizing a wiper, may alsobe massaged by wiper 11 along the inside of second stage drum 9A. Inthis manner, the sludge may be pushed into stage III, including drum 9B.In one embodiment, third stage drum 9B may rotate at about the samespeed as drums 9 and 9A, but it may have a larger diameter. In oneembodiment, third stage drum 9B may have about a 20 inch insidediameter. This increase in diameter imparts a higher centrifugal forceon the drying sludge. The holes/slots in the walls of third stage drum9B may be the same size or larger than the holes/slots of second stagedrum 9A, giving a larger open area for the water and liquids to bereleased through the third stage drum 9B wall.

[0033] As the sludge is dried in third stage drum 9B it may be moved byscrew flighting 10 and, in embodiments utilizing a wiper, may also bemassaged by wiper 11 along the inside of the drum 9B. In this manner,the sludge may be pushed into stage IV, including fourth stage drum 9C.In one embodiment, fourth stage drum 9C may rotate at the same speed asdrums 9-9B, but it may have a larger diameter. In one embodiment, fourthstage drum may have about a 24 inch inside diameter. This increase indiameter imparts a higher centrifugal force on the drying sludge. Theholes/slots in the walls of fourth stage drum 9C may be the same size orlarger than the holes/slots of third stage drum 9B, giving a larger openarea for the water and liquids to be released through the fourth stagedrum 9C wall.

[0034] As the sludge is dried in fourth stage drum 9C, it may be movedby the screw flighting 10, and in embodiments utilizing a wiper, mayalso be massaged by the wiper 11 along the inside of the fourth stagedrum 9C. In this manner, the sludge may be pushed out the discharge endof the apparatus, and if inclined, may be directly loaded into anappropriate transport or bin without the need for a separate conveyor.

[0035] With the benefit of the present disclosure those of skill in theart will recognize that more or fewer stages may be utilized to de-watersludge. Specifically, one may utilize only a first and second stage drum9 and 9A. One may also choose to only utilize a first stage drum 9.Alternatively, one may utilize more than the four stage systemillustrated herein. For instance, one may to choose any number oradditional stages to achieve a desirable degree of de-watering. In suchembodiments, the relative sizes of each drum stage may vary as well. Forinstance, the increase in diameter from one stage to another may belarge or slight, according to need and/or application.

[0036] The discharge end 16, of drums 9-9C is where dried sludge exitsthe drying process. In one embodiment, this end may contain a supportbracket 17 configured to hold drums 9-9C in place. Support bracket 17also may be configured to allow the drums to rotate about thecenterline, longitudinal axis 18 via the use of a bearing assembly suchas assembly 19. In the illustrated embodiment, support bracket 17 notonly holds the drums 9-9C in place around main shaft 7 and longitudinalaxis 18, but it also includes sludge outlet holes 13 and wiper fins 28.Fins 28 may be configured to wipe sludge from discharge cowling 29, sothat it may exit housing 1, at the outlet 30.

[0037] In the illustrated embodiment, bearing assembly 20 holds thedischarge end of the apparatus at main shaft 7 to housing 1. This allowsmain shaft 7, screw shaft 8, flighting 10, wiper 11, and drums 9-9C torotate inside the housing 1. The water and liquids forced out of thesludge slurry as it is dried may fall to the bottom of the housing 1 andmay drain out discharge pipes and/or holes 21, which may be located inthe bottom of the housing 1.

[0038] In the illustrated embodiment, the drums 9-9C may be bolted tolower end plate support 26 and bearing 27 through a suitable flangeconnection with centering pilots so as to ensure rotation about fixedlongitudinal axis 18. The drums may be bolted to the upper supportbracket 17 and bearing 19 through a suitable flange connection withcentering pilots to ensure a rotation about a fixed longitudinal axis18. Each of the drums 9-9C may be bolted to each other through flangeconnections, or any other suitable coupling device. For example,centering pilots and accepting mating surfaces may be utilized to ensurethat each drum run true and around the same longitudinal axis 18.

[0039] In one embodiment, a de-watering apparatus may also be equippedwith an internal washing system. Such a system may be configured tocontinuously wash holes/slots of drums 9-9C from the inside. In such anembodiment, screw shaft 8 may be set up with two or more sets of screwflightings 10, which may run parallel to each other. Flighting 10 may beequipped with wiper 11, as previously described One area between tworows of flightings 10 may be blocked off at or adjacent inlet holes 12to provide an area running along the entire length of the screwflightings 10 and wipers 11 that is free from sludge, and which isisolated by the wipers 11. Screw shaft 8 may be equipped with washnozzles 22, which may be spaced as needed, along the entire length ofthe screw shaft 8 in this sludge free area. Wash water may be fed fromthe discharge end of the apparatus into main shaft 7. Main shaft 7 mayinclude a dividing plate 25, located just above inlet holes 12 thatisolates the sludge-feed end of the main shaft 7 from the water-feed endof shaft 7. Main shaft 7 may also contain water outlet holes 16 to allowwash water to enter the space between main shaft 7 and screw shaft 8 andout through the wash nozzles 22. In embodiments utilizing a differentialspeed technique, it will be understood that as screw shaft 8 rotates ata different speed than drums 9-9C, the wash nozzles 22 may wash theentire inside surface of drums 9-9C. The wash water may exit theholes/slots in drums 9-9C, exiting along with water and liquids from thesludge slurry being dried in the apparatus. In this embodiment, the washwater may be fed into main shaft 7 via any suitable means. Asillustrated, the introduction of wash water may be achieved with pipe 23through swivel joint 24.

[0040] While the present disclosure may be adaptable to variousmodifications and alternative forms, specific embodiments have beenshown by way of example and described herein. However, it should beunderstood that the present disclosure is not intended to be limited tothe particular forms disclosed. Rather, it is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims.

[0041] Moreover, the different aspects of the disclosed apparatus andmethods be, utilized in various combinations and/or independently. Thusthe invention is not limited to only those combinations shown herein,but rather may include other combinations. Those of skill in the artwill understand that numerous other modifications may be made to thedisclosed method and apparatus, but all such similar substitutes andmodifications are deemed to be within the spirit, scope and concept ofthe invention.

What is claimed is:
 1. An apparatus for de-watering sludge, comprising:an outer housing defining a longitudinal axis; a main shaft configuredto rotate about the longitudinal axis; a screw shaft coupled to the mainshaft and configured to rotate about the longitudinal axis; a firststage drum positioned between the outer housing and the screw shaft, thefirst stage drum configured to rotate about the longitudinal axis, thefirst stage drum having a first drum diameter; a second stage drumcoupled to the first stage drum, the second stage drum configured torotate about the longitudinal axis, the second stage drum having asecond drum diameter greater than the first drum diameter; an inletconfigured to introduce the sludge to a first area defined by an outersurface of the screw shaft and an inner surface of the first stage drum;and screw flighting coupled to the screw shaft, the screw flightingconfigured to rotate about the longitudinal axis to transport the sludgelongitudinally from the first area to a second area defined by an outersurface of the screw shaft and an inner surface of the second stagedrum, the second area being larger than the first area.
 2. The apparatusof claim 1 , wherein the main shaft and the screw shaft are eachconfigured to rotate at a first rate and wherein the first stage drumand the second stage drum are each configured to rotate at a secondrate.
 3. The apparatus of claim 2 , wherein the first rate is less thanthe second rate.
 4. The apparatus of claim 2 , wherein the first rateequals the second rate.
 5. The apparatus of claim 1 , wherein the mainshaft has a substantially constant outer diameter and wherein the screwshaft has a substantially constant outer diameter.
 6. The apparatus ofclaim 1 , further comprising a wiper coupled to the screw flighting, thewiper configured to clean an inner surface of the first stage drum andto roll the sludge from the first area to the second area.
 7. Theapparatus of claim 1 , wherein the first stage drum comprises a firstslot and the second stage drum comprises a second slot, each of thefirst and second slots comprising a smaller opening on an inner surfaceof the drums than on an outer surface of the drums.
 8. The apparatus ofclaim 7 , wherein the first slot is smaller than the second slot.
 9. Theapparatus of claim 7 , wherein the first slot is about the same size asthe second slot.
 10. The apparatus of claim 1 , further comprising: athird stage drum coupled to the second stage drum, the third stage drumconfigured to rotate about the longitudinal axis, the third stage drumhaving a third drum diameter greater than the second drum diameter;wherein the screw flighting is configured to transport the sludgelongitudinally from the second area to a third area defined by an outersurface of the screw shaft and an inner surface of the third stage drum,the third area being larger than the second area.
 11. The apparatus ofclaim 10 , further comprising: a fourth stage drum coupled to the thirdstage drum, the fourth stage drum configured to rotate about thelongitudinal axis, the fourth stage drum having a fourth drum diametergreater than the third drum diameter; wherein the screw flighting isconfigured to transport the sludge longitudinally from the third area toa fourth area defined by an outer surface of the screw shaft and aninner surface of the fourth stage drum, the fourth area being largerthan the third area.
 12. The apparatus of claim 1 , further comprising awash nozzle coupled to the screw shaft.
 13. The apparatus of claim 1 ,wherein the outer housing is inclined.
 14. An apparatus for de-wateringsludge, comprising: an outer housing defining a longitudinal axis; amain shaft configured to rotate about the longitudinal axis; a screwshaft coupled to the main shaft and configured to rotate about thelongitudinal axis; a drum positioned between the outer housing and thescrew shaft, the drum configured to rotate about the longitudinal axis,the drum having a slot comprising a smaller opening on an inner surfaceof the drum than on an outer surface of the drum; an inlet configured tointroduce the sludge to an area defined by an outer surface of the screwshaft and an inner surface of the drum; screw flighting coupled to thescrew shaft, the screw flighting configured to rotate about thelongitudinal axis to transport the sludge longitudinally along the drum;and a wiper coupled to the screw flighting, the wiper configured toclean an inner surface of the drum and to roll the sludge along thedrum.
 15. An apparatus for de-watering sludge, comprising: an outerhousing defining a longitudinal axis; a main shaft configured to rotateabout the longitudinal axis; a screw shaft coupled to the main shaft andconfigured to rotate about the longitudinal axis; a wash nozzle coupledto the screw shaft; a first stage drum positioned between the outerhousing and the screw shaft, the first stage drum configured to rotateabout the longitudinal axis, the first stage drum having a first drumdiameter and a first slot, the first slot comprising a smaller openingon an inner surface of the first stage drum than on an outer surface ofthe first stage drum; a second stage drum coupled to the first stagedrum, the second stage drum configured to rotate about the longitudinalaxis, the second stage drum having a second drum diameter greater thanthe first drum diameter and a second slot, the second slot comprising asmaller opening on an inner surface of the second stage drum than on anouter surface of the second stage drum; an inlet configured to introducethe sludge to a first area defined by an outer surface of the screwshaft and an inner surface of the first stage drum; screw flightingcoupled to the screw shaft, the screw flighting configured to rotateabout the longitudinal axis to transport the sludge longitudinally fromthe first area to a second area defined by an outer surface of the screwshaft and an inner surface of the second stage drum, the second areabeing larger than the first area; and a wiper coupled to the screwflighting, the wiper configured to clean an inner surface of the firststage drum and to roll the sludge from the first area to the secondarea.
 16. The apparatus of claim 15 , wherein the main shaft and thescrew shaft are each configured to rotate at a first rate and whereinthe first stage drum and the second stage drum are each configured torotate at a second rate.
 17. The apparatus of claim 16 , wherein thefirst rate is less than the second rate.
 18. The apparatus of claim 16 ,wherein the first rate equals the second rate.
 19. A method forde-watering sludge, comprising: rotating a main shaft about alongitudinal axis at a first rate; rotating a screw shaft coupled to themain shaft about the longitudinal axis at the first rate; rotating screwflighting coupled to the screw shaft about the longitudinal axis at thefirst rate; rotating a first and second stage drum about thelongitudinal axis at a second rate, the first and second stage drumsbeing positioned between an outer housing and the screw shaft;introducing the sludge to a first area defined by an outer surface ofthe screw shaft and an inner surface of the first stage drum; removingmoisture from the sludge through a first slot coupled to the first stagedrum; transporting the sludge with the screw flighting from the firstarea to a second area defined by an outer surface of the screw shaft andan inner surface of the second stage drum, the second area being largerthan the first area; and removing moisture from the sludge through asecond slot coupled to the second stage drum.
 20. The method of claim 19, wherein the first rate is less than the second rate.
 21. The method ofclaim 19 , wherein the first rate equals the second rate.
 22. The methodof claim 19 , further comprising cleaning an inner surface of the firststage drum with a wiper coupled to the screw flighting.
 23. The methodof claim 19 , further comprising cleaning an inner surface of the firststage drum with a wash nozzle coupled to the screw shaft.
 24. The methodof claim 19 , further comprising: rotating a third stage drum about thelongitudinal axis at the second rate, the third stage drum beingpositioned between an outer housing and the screw shaft; transportingthe sludge with the screw flighting from the second area to a third areadefined by an outer surface of the screw shaft and an inner surface ofthe third stage drum, the third area being larger than the second area;and removing moisture from the sludge through a third slot coupled tothe third stage drum.
 25. The method of claim 24 , further comprising:rotating a fourth stage drum about the longitudinal axis at the secondrate, the fourth stage drum being positioned between an outer housingand the screw shaft; transporting the sludge with the screw flightingfrom the third area to a fourth area defined by an outer surface of thescrew shaft and an inner surface of the fourth stage drum, the fourtharea being larger than the third area; and removing moisture from thesludge through a fourth slot coupled to the fourth stage drum.